AIO_READ(3C) Standard C Library Functions AIO_READ(3C)
NAME
aio_read - asynchronous read from a file
SYNOPSIS
#include <aio.h>
int aio_read(
struct aiocb *aiocbp);
DESCRIPTION
The
aio_read() function allows the calling process to read
aiocbp->
aio_nbytes from the file associated with
aiocbp->
aio_fildes into
the buffer pointed to by
aiocbp->
aio_buf. The function call returns when
the read request has been initiated or queued to the file or device (even
when the data cannot be delivered immediately). If
_POSIX_PRIORITIZED_IO is defined and prioritized I/O is supported for this file, then the
asynchronous operation is submitted at a priority equal to the scheduling
priority of the process minus
aiocbp->
aio_reqprio. The
aiocbp value may
be used as an argument to
aio_error(3C) and
aio_return(3C) in order to
determine the error status and return status, respectively, of the
asynchronous operation while it is proceeding. If an error condition is
encountered during queuing, the function call returns without having
initiated or queued the request. The requested operation takes place at
the absolute position in the file as given by
aio_offset, as if
lseek(2) were called immediately prior to the operation with an
offset equal to
aio_offset and a
whence equal to
SEEK_SET. After a successful call to
enqueue an asynchronous I/O operation, the value of the file offset for
the file is unspecified.
The
aiocbp->
aio_sigevent structure defines what asynchronous notification
is to occur when the asynchronous operation completes, as specified in
signal.h(3HEAD).
The
aiocbp->
aio_lio_opcode field is ignored by
aio_read().
The
aiocbp argument points to an
aiocb structure. If the buffer pointed
to by
aiocbp->
aio_buf or the control block pointed to by
aiocbp becomes
an illegal address prior to asynchronous I/O completion, then the
behavior is undefined.
Simultaneous asynchronous operations using the same
aiocbp produce
undefined results.
If
_POSIX_SYNCHRONIZED_IO is defined and synchronized I/O is enabled on
the file associated with
aiocbp->
aio_fildes, the behavior of this
function is according to the definitions of synchronized I/O data
integrity completion and synchronized I/O file integrity completion.
For any system action that changes the process memory space while an
asynchronous I/O is outstanding to the address range being changed, the
result of that action is undefined.
For regular files, no data transfer will occur past the offset maximum
established in the open file description associated with
aiocbp->
aio_fildes.
RETURN VALUES
The
aio_read() function returns
0 to the calling process if the I/O
operation is successfully queued; otherwise, the function returns
-1 and
sets
errno to indicate the error.
ERRORS
The
aio_read() function will fail if:
EAGAIN The requested asynchronous I/O operation was not queued due to
system resource limitations.
Each of the following conditions may be detected synchronously at the
time of the call to
aio_read(), or asynchronously. If any of the
conditions below are detected synchronously, the
aio_read() function
returns
-1 and sets
errno to the corresponding value. If any of the
conditions below are detected asynchronously, the return status of the
asynchronous operation is set to -1, and the error status of the
asynchronous operation will be set to the corresponding value.
EBADF The
aiocbp->
aio_fildes argument is not a valid file descriptor
open for reading.
EINVAL The file offset value implied by
aiocbp->
aio_offset would be
invalid,
aiocbp->aio_reqprio is not a valid value, or
aiocbp->
aio_nbytes is an invalid value.
In the case that the
aio_read() successfully queues the I/O operation but
the operation is subsequently canceled or encounters an error, the return
status of the asynchronous operation is one of the values normally
returned by the
read(2) function call. In addition, the error status of
the asynchronous operation will be set to one of the error statuses
normally set by the
read() function call, or one of the following values:
EBADF The
aiocbp->
aio_fildes argument is not a valid file
descriptor open for reading.
ECANCELED The requested I/O was canceled before the I/O completed due
to an explicit
aio_cancel(3C) request.
EINVAL The file offset value implied by
aiocbp->
aio_offset would be
invalid.
The following condition may be detected synchronously or asynchronously:
EOVERFLOW The file is a regular file,
aiobcp->
aio_nbytes is greater
than 0 and the starting offset in
aiobcp->
aio_offset is
before the end-of-file and is at or beyond the offset
maximum in the open file description associated with
aiocbp->
aio_fildes.
USAGE
For portability, the application should set
aiocb->aio_reqprio to
0.
The
aio_read() function has a transitional interface for 64-bit file
offsets. See
lf64(7).
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | MT-Safe |
+--------------------+-------------------+
|Standard | See
standards(7). |
+--------------------+-------------------+
SEE ALSO
close(2),
exec(2),
exit(2),
fork(2),
lseek(2),
read(2),
write(2),
aio_cancel(3C),
aio_return(3C),
lio_listio(3C),
aio.h(3HEAD),
siginfo.h(3HEAD),
signal.h(3HEAD),
attributes(7),
lf64(7),
standards(7) February 5, 2008
AIO_READ(3C)